1. Field of the Invention
The present invention relates to an alarm device and alarm system which detects an abnormal condition such as a fire and emits an alarm, and also wirelessly transmits an alarm signal to other alarm devices to facilitate linked alarm output.
Priority is claimed on Japanese Patent Application No. 2007-315976, Japanese Patent Application No. 2008-116708, and Utility Model Application No. 2008-002726, the contents of which are incorporated herein by reference.
2. Description of Related Art
[First Background Art]
Conventionally, alarm devices such as fire alarms and gas detectors have been used which detect an abnormal condition such as a fire or gas leak and emit an alarm. Furthermore, alarm systems have been used in which a plurality of such alarm devices are provided, and when an abnormal condition is detected in any one of these alarm devices and the alarm device outputs an alarm, the other alarm devices also output an alarm in a linked manner. A known example of such an alarm device comprises a transmission device for transmitting linkage instructions to an external destination, and a reception device for receiving linkage instructions from an external source, and emitting an alarm upon detecting an abnormal condition or receiving a linkage instruction from an external source (see Japanese Unexamined Patent Application, First Publication No. 2007-213507, for example).
[Second Background Art]
Furthermore, conventionally, household alarm devices (hereafter “alarm devices”) which detect abnormal conditions such as fires or gas leaks in a residence and issue an alarm have become prevalent, and in recent years, there is a growing trend towards monitoring for abnormal conditions such as a fire on a room-by-room basis by installing a plurality of alarm devices throughout a single residence (see Japanese Unexamined Patent Application, First Publication No. 2007-094719, for example).
When a plurality of alarm devices are installed in a single residence in this manner, a person who is present in a different room from the room where the abnormal condition occurred may not hear the alarm sound, giving the fire or other problem a chance to spread. Therefore, by connecting each alarm device to the others using wires, when a particular alarm device detects a fire and issues an alarm, the alarm signal is sent from this alarm device to the other alarm devices so that the alarm is emitted simultaneously, thereby realizing a linked alarm system.
However, because providing a wired connection between each alarm requires that wiring be installed, a problem arises in terms of increased costs. This problem can be resolved by employing wireless alarm devices. Furthermore, because the ICs used in modern wireless circuits have very low power consumption, even when operating in a state of constant readiness to receive alarm signals from other alarm devices, battery life that is sufficient from a practical standpoint, for example five years or longer, is assured. Accordingly, an environment that enables the practical use of wireless alarm devices is steadily taking shape.
Incidentally, with wireless alarm devices, because there is no way of knowing when an alarm signal indicating an abnormal condition will be received from one of the other alarm devices, the reception circuit must be in constant readiness to receive an alarm signal. However, because this increases power consumption, reception behavior takes place at a predetermined reception cycle.
FIG. 17 is a timing chart showing the transmission behavior and reception behavior of a conventional wireless alarm device. In FIG. 17, (A) shows the behavior of a transmitting side alarm device, (B) shows the behavior of a receiving side alarm device, and (C) shows the alarm output behavior of the receiving side alarm device.
As shown in (B) in FIG. 17, the alarm device on the receiving side performs intermittent reception behavior in a repeating cycle T112 (=T101+T102) consisting of reception behavior for a duration T101 interposed with a rest time T102. On the other hand, as shown in (A) in FIG. 17, the alarm device on the transmitting side, upon detecting an abnormal condition, transmits a detection signal (alarm signal) indicating the abnormal condition continuously and repeatedly for a duration T104.
The transmission time T104 is set to a time equal to or longer than the intermittent reception cycle T112 (=T101+T102), so that regardless of when transmission is initiated, the reception behavior that spans a time T101 occurs at least once during the transmission time T104, enabling the detection signal from the transmission side alarm device to be reliably received.
As a result of this intermittent reception behavior, there is no need for the reception circuitry to remain in a state of constant readiness, and the power consumption of the reception circuitry can be reduced, thereby guaranteeing battery life exceeding five years in wireless alarm devices.
However, in an alarm device and alarm system according to the first background art described above, in order for the other alarm devices to perform alarm output in a linked manner when an alarm is output from an arbitrary alarm device within the alarm system, the alarm signal transmitted from the alarm device which detected the occurrence of the abnormal condition must be received by the other alarm devices. Therefore, the reception device of each alarm device is operated on a constant or intermittent basis so that the alarm device can receive the alarm signals transmitted from the other alarm devices.
In particular, in an alarm device driven by an internal power source such as a battery, to reduce power consumption, the reception device needs to be operated intemittently, with a large interval provided between each intermittent operation. As a result, in the interval after an alarm signal is transmitted from the alarm device that detected the occurrence of the abnormal condition until the alarm signal is received by the other alarm devices, in some cases a length of time equivalent to the time interval between intermittent operations is required. Accordingly, a problem occurs in that a lack of synchronization occurs between the timing at which the alarm signal is output from the alarm device that detected the occurrence of the abnormal condition, and the timing at which an alarm is output by the other alarm devices that received the alarm signal transmitted from this alarm device. For example, when a user runs an operation test after installing the alarm devices, the delay between output of the alarm signal by the alarm device being tested and alarm output by the other alarm devices may be misconstrued as a fault in the alarm device.
Accordingly, an alarm device and alarm system is desired which suppresses gaps in alarm output timing between the alarm device that transmits the alarm signal and the alarm devices that receive the alarm signal.
Furthermore, in the wireless alarm device that performs intermittent reception behavior described in the second background art, in the same manner, depending on the timing with which the alarm device on the transmission side initiates signal transmission, the timing with which the alarm device on the receiving side receives the signal and starts linked alarm output can present significant delays relative to initiation of alarm output by the transmission side alarm device.
FIG. 18 is a timing chart showing the transmission timing which produces the greatest delay in terms of initiating alarm output on the receiving side. In FIG. 18, (A) shows the behavior of the transmission side alarm device, (B) shows the behavior of the reception side alarm device, and (C) shows the alarm output behavior of the reception side alarm device. As shown in FIG. 18, if the alarm device on the transmission side initiates signal transmission immediately after the alarm device on the receiving side performs reception behavior at a time T101, the next reception behavior takes place after a time T102 has elapsed. Accordingly, the delay time T100d from alarm initiation on the transmission side until linked alarm initiation on the reception side is long, causing a problem in that linked alarm output is delayed.
For example, the rest time T102 in the intermittent reception is 10 to 20 seconds or thereabouts, and if, to enhance reliability, a system whereby an alarm is emitted after an alarm signal is received three times is adopted, the delay time T100d from when alarm output is initiated on the transmission side until linked alarm output is initiated on the reception side is 30 to 60 seconds or thereabouts, significantly delaying linked alarm output.
Accordingly, it is desired to provide an alarm device which suppresses alarm delays associated with intermittent reception on the reception side, and achieves prompt linked alarm output.
In consideration of the circumstances disclosed in the first and second background art, an object of the present invention is to provide an alarm device and alarm system which can resolve the problems associated with a lack of synchronization in the transmission and reception timing of the alarm signal between alarm devices.